Effervescent denture cleansers have been long known in the art. Most of those presently on the market derive their cleansing efficiency mainly from peroxy compounds which provide active oxygen. While the active oxygen provides a good bleaching action, it has relatively poor plaque removing properties. Various peroxygen type denture cleansers are described in U.S. Pat. Nos. 2,498,343; 2,498,344; 2,931,776 and 3,243,377.
Another type of denture cleanser described in U.S. Pat. No. 3,113,111 derives its cleansing efficacy from an active chloride source and has good plaque removing properties. The product, however, is not effervescent and must be stirred mechanically to dissolve. An effervescent denture cleansing composition which releases hypochlorite/chlorine on contact with water is disclosed in U.S. Pat. No. 3,936,385. The product has good plaque removing properties and dissolves without stirring. However, it is not fully acceptable because of the chlorine odor associated with the product and its tendancy to corrode metals. Efforts to mask odor using fragrances have been unsuccessful because of the strong hypochlorite odor.
Recent improvements in these hypochlorite type of denture cleansing composition include the disclosure of U.S. Pat. No. 4,362,639 to Eoga. The denture cleanser of that disclosure include ammonium ion compounds which inhibit hypochlorite odor emission and inhibit metal tarnish or corrosion. However, amine compounds may result in the generation of undesirable chloramines.
The art is replete with references which teach the reaction of hypochlorite solutions with a wide range of compounds. An article entitled "Kinetic Studies on the Chloramines," authored by Ira Weil and J. Carrell Morris, J. Am. Chem. Soc, 71, 1644-1671 (1949) discloses reactions of ammonia and primary amines witn hypochlorite. The reaction of hydrogen peroxide and hypochlorous acid has been studied; see for example "The Interaction of Hydrogen Peroxide and Hypochlorous Acid in Acidic Solutions Containing Chloride Ion ", Connick, R. R., J. Am. Chem. Soc., 69, 1509-1514 (1947). Similarly the reactions of iodates and nitrites are taugnt in the art; see "The Oxidation of Nitrite and Iodate Ions by Hypochlorite Ions," Lister, M. W. and Rosenblum, P., Canadian Journal of Chemistry, 39, 1645-1651 (1961). Hydrazine dihydrochloride has been taught as a chlorine scavanger. See "Chlorine Scavenger for HCL Gas Streams," page 539 Merck Index 8th Ed., 1968. Guanidine has also been used to scavenge chloride in sewer gases.
U.S Pat. No. 4,295,985 discloses a soap which removes chlorine odor from the skin and hair of bathers. The composition is said to neutralize chlorine (as hypochlorite). Compounds taught to be suitable neutralizing agents are sodium nitrite, sodium sulfite, sodium thiosulfate, urea, thiourea, ascorbic acid, hydrazine, hydroxylamine, pyrrole, sodium terrocyanide, hydroquinone, formaldehyde, furtural, sodium hypophosphate and sodium hydrosulfite.
In general, the prior art approach has been to add the deodorizing agent to the denture cleansing composition. As such, it immediately begins to reduce the available hypochlorite. Hence, either reduced efficiency must be accepted or substantially larger amounts of cleansing agent, at increased costs, must be utilized to achieve the desired effect.
Various methods are taught in the art for delaying the activity of a particular component of the denture cleansing composition. For example, U.S. Pat. No. 3,952,107 discloses a two part tablet which preferentially releases an enzyme to attack the proteinaceous materials which are loosely bonded to plaque. Subsequently, an oxygen generating agent is released to complete the cleaning. The delay time between each activation step is disclosed to be about 60 to 120 seconds. The time release is accomplished by consideration of the relative thickness of the two layers, the proportion of the effervescent producing composition in each layer and the particle size of certain ingredients in each layer. Similarly, U.S. Pat. No. 4,256,999, discloses a two layer denture cleansing tablet, each of which disintegrate at controlled rates to give improved cleaning efficiency. Various techniques, including the use of silicic acid and polyvinyl pyrrolidone, to control the release rate are taught.
There is no teaching in the art of a method for preparing a substantially odor free, hypochlorite releasing denture cleanser.